Aviation safety investigations & reports

Bell Helicopter Co 206L-1, VH-WEB

Summary

The pilot of a Bell Long Ranger 206L-1 was returning to base
following an agricultural crop-spraying task. While transiting a
ridgeline of the Connors Mountain Range, the helicopter collided
with wires and impacted the ground in a densely wooded area about
200 metres beyond the wires.

The pilot received fatal injuries and the helicopter was
destroyed in a post-crash fire. Witnesses had observed a helicopter
approaching the ridgeline at a very low height, and reported that,
shortly afterwards, a pall of black smoke was visible.

The helicopter had struck two three-strand lightweight
high-tensile steel wires of a powerline supplying a repeater site.
A wire strike protection system (WSPS) had not been fitted to the
helicopter. The wires were aligned on 060 degrees magnetic, with a
maximum height of 31.5 metres for the upper wire and 30.1 metres
for the lower wire. The position of the wires was not annotated on
the relevant Visual Terminal Charts and they did not have high
visibility devices attached. Company employees said that it was
usual for the pilot to fly at a low height when transiting to and
from the work location.

Examination of the wreckage indicated that the helicopter had
struck the ground with a vertical downward force and at a low
forward speed on a heading of 030 degrees magnetic. The main rotor
blades were severely fractured by contact with the surrounding
trees. The tail boom was severed just forward of the horizontal
stabiliser and the tail rotor gearbox and blades were intact. Fire
destroyed the helicopter cabin and heavily damaged the engine
compartment and upper transmission deck. Examination of the engine
to determine pre-impact airworthiness was limited due to fire
damage.

The white-colour coded main rotor pitch control rod, broken
sections of the windscreen, and the top section of the main
transmission cowling were found along the flight path about 75
metres before the main wreckage. One main rotor blade severed the
upper wire. The lower wire contacted the fuselage in the area of
the forward canopy, progressed up to the fibreglass transmission
cowl, and separated the top lip of the cowl. That wire, together
with the separated section of cowl, then contacted the flight
controls above the main rotor swashplate, causing static overload
and separation of the white colour-coded main rotor pitch change
rod. Directional control of the helicopter was lost following the
separation of the control rod.

The investigation found no evidence to suggest that the
helicopter was not fully serviceable at the time of the accident.
It is likely that the oblique angle of approach to the wires
limited the pilot's ability to detect them, and "contour flying"
offered minimal reaction time for the pilot to avoid the wires had
they been detected.

A review of the Australian Transport Safety Bureau (ATSB)
database for the period January 1, 1995, to March 3, 2001, revealed
six fatal agricultural helicopter accidents in Australia. These
accidents represented seven fatalities and 42% of all fatal
helicopter wire-strike accidents during the period.

Previous safety action

The Australian Transport Safety Bureau (then known as the Bureau
of Air Safety Investigation) made a recommendation in 1995 to the
Civil Aviation Safety Authority (then known as the Civil Aviation
Authority) following a similar fatal accident related to a wire
strike of a helicopter. The recommendation, R19950120, stated:

The Bureau of Air Safety Investigation (BASI) recommends that
the Civil Aviation Authority (CAA):

(1) Require the fitment of approved WSPS kits for all
helicopters engaged in low flying activities for which a kit
exists; and

(2) That only agricultural spray kits compatible with WSPS be
approved for fitment to these helicopters.

The CAA response to the recommendation was as follows:

While WSPS may have been of benefit in this and similar
accidents, the Authority believes that the fitment of WSPS should
not be mandatory. However, the CAA is of the view that it should be
strongly encouraged when suitable equipment is available.

The CAA in conjunction with BASI, is prepared to undertake an
industry education program highlighting the hazards associated with
low level helicopter operations as well as the advantages provided
by the fitment of WSPS to appropriate helicopters.

On 15 May 1996, BASI classified the recommendation CLOSED- No
further action, however, continued to monitor the number of wire
strike accidents.

Safety Action

Although the Civil Aviation Safety Authority (CASA) implemented training programs to educate the industry on the hazards associated with low level helicopter operations, it is believed that WSPS kits may yet prove beneficial in mitigating helicopter wire strike accidents.

As a result of this investigation, and after a review of the ATSB accident database statistics relating to agricultural helicopter wire strike fatal accidents, the ATSB is concerned that fatalities are continuing to occur in agricultural helicopter operations despite the earlier recommendation (R19950120). The ATSB therefore issues the following recommendation.

R20010083

The ATSB recommends that CASA:

(i) Require the fitment of approved Wire Strike Protection System kits for all helicopters engaged in low flying activities for which a kit exists; and

(ii) That only agricultural spray kits compatible with Wire Strike Protection Systems be approved for fitment to these helicopters.